Function: vecprod
Section: linear_algebra
C-Name: vecprod
Prototype: G
Help: vecprod(v): return the product of the components of the vector v.
Doc: return the product of the components of the vector $v$. Return $1$ on an
 empty vector.
 \bprog
 ? vecprod([1,2,3])
 %1 = 6
 ? vecprod([])
 %2 = 1
 @eprog
